Abstract: In order to probe into the common character of Nymphaeales and Alismatales in early stage of ontogeny, developmental process from seed to seedling of N. tetragona var.crassifolia was observed in this study. The shoot ends developments before the root ends in seed embryo. When the seed germinates, the hypocotyl appears firstly and swells around the end of it, and some hairs (hypocolyl hair) arise from the swelling. At the same time, the radicle begins to differentiate and grow up a primary root. The primary root is ephemeral but the nodal roots are long-lived and thicker. When the floating leaves emerge, the portion bellow the first node of rhizome is withered. Every seedling organs are of aerenchyma, etc. All of these characters are similar to Euryale ferox, Alisma orientale and Hydrilla verticillala.

Key words: Nymphaea tetragona var. crassifolia, seed, seedling, developmental morphology